Mechanism of the methylene transfer reaction. C-C activation and reductive elimination in one system. A DFT study

DFT calculations were employed to investigate the methylene transfer reaction mechanism in a model system related to the experimental Rh/PCP ligand system previously reported by us. The computationally established mechanism is in accordance with the experimental results. It was found to be a C-C reductive elimination/C-C oxidative addition sequence in which the C-C reductive elimination is the rate-determining step. The C-C activation reaction was found to take place by two different routes; both proceed through the initial formation of the eta(2)-arene complex 2. In one pathway, C-C activation takes place from an agostic C-H complex intermediate, and in the other, it occurs from the eta(2)-arene complex directly. In both intermediates the C-C bond is predirected to the metal center. The methylene transfer reaction outcome is governed by thermodynamic factors. However, changing the thermodynamic factors might lead to the reverse methylene transfer reaction becoming kinetically accessible. The reverse reaction is relevant to the design of a potential catalytic methylene transfer system.